1. Field of the Invention
This invention pertains generally to optical imaging, and more particularly to high-speed optical imaging using dispersive Fourier-transform imaging.
2. Description of Related Art
A barcode is a machine-readable binary representation of information which normally appears as a series of low reflectance bars (e.g., dark or black bars) on a high reflectance background (e.g., light or white background). A measurable difference in optical properties of the bars (e.g., reflectance of dark bars in contrast to light bars) is converted to a binary representation. For example, with the dark bars corresponding to 0's with the white spaces therebetween corresponding to 1's, or vice-versa, depending on the decoding software. Barcodes can be read by optical scanners called barcode readers which measure optical reflections from the black bars or white spaces when a probe beam is incident on them.
Since their introduction, barcodes have become indispensable in labeling and inventory management. Some modern applications of barcodes, include: (a) product labeling and automated detection; (b) ticketing and permits; (c) movement and flow, such as mail, packages, airplane luggage, rental cars, and nuclear waste; (d) document management, including imaging, filing and indexing; (e) blood bank information systems; (f) tracking in bee research; (g) collecting parcel data from multiple networked sources and tracking thereto. One of ordinary skill in the art will appreciate that barcode applications have become ubiquitous in our modern society.
A barcode reader is an essential part of barcode technology. A conventional reader consists of a scanner, a decoder (either built-in or external), and a cable used to connect the reader with a processing device (e.g., computer) for processing the digital signals. A barcode reader is an optoelectronic device that measures optical reflections from barcodes, such as consisting of non-reflective black bars and reflective white spaces. There are different types of barcode readers available in the marketplace, which use slightly different methods for reading and decoding barcodes. Barcodes can be of a one-dimensional variety as described with bars and lines, or may be two-dimensional with dots or other small spatially constrained symbols contained on a two-dimensional field.
One form of barcode reader is a pen-type reader, in which a continuous-wave optical source and a photodiode receptor are proximal one another, such as in the tip of a pen or wand. To read a barcode, the tip of the pen is moved across the bars in a steady motion. A voltage waveform that represents the bar and space pattern in the barcode is generated in response to photodiode detection of changing light power reflected back from the bars as they are exposed to the moving incident light. The waveform detected by the photodiode is decoded by the scanner in a manner similar to the way Morse code dots and dashes are decoded.
Another form of barcode reader is a laser scanner, which works much as a pen type reader, except that it employs either a reciprocating mirror or a rotating prism to scan the laser beam back and forth across the barcode. Just like the pen type reader, a photodiode is used to measure the power of the light reflected back from the barcode. In both pen type readers and laser scanners, the light emitted by the reader is tuned to a specific wavelength and the photodiode is designed to detect only this wavelength.
Another form of reader is a CCD reader, in which a charge-coupled device (CCD) reader, or alternatively a CMOS active pixel reader, utilizes an array of optical sensors lined up in a row in the head of the reader. The CCD reader measures the light reflected from a barcode, generating a voltage pattern identical to the pattern in the barcode by measuring the voltages across each sensor in the row. One important difference between a CCD reader and a pen type or laser scanner is that the CCD reader measures the reflection of ambient light from the barcode while pen or laser scanners measure reflected light at the specific wavelength which originated from the scanner itself.
Another form of reader is a camera based reader, in which a camera captures a two-dimensional image of the barcode. These are particularly well-suited for use with reading two-dimensional barcodes, although they can technically read either type of bar code. It will be appreciated that for a given geometric resolution (e.g., based on minimum line or pixel spacing) the information density of a two-dimension barcode can far exceed that of a one-dimensional bar-code which is only scanned across a single direction. By way of example, an image of the barcode is captured by a small CCD or CMOS camera imager and decoded using digital image processing techniques.
Although barcode readers are useful for keeping track of a large number of items, the conventional barcode technology has its limitation in speed when it requires tracking of a considerably large number of items (e.g., on the order of millions) due to their slow reading and decoding process. Conventional barcode readers have a scan rate on the order of several hundred scans per second. Even the fastest barcode reader is limited to a rate of about one thousand scans per second. The speed limitation in scanners is largely in response to the need of scanning the source light across the barcode, while in imaging readers the image frame rate limits the number of scans per second.
The speed limit of conventional barcode readers combined with the conventional digital signal processing prohibits one from tracking a considerably larger number of items, especially in applications including the fields of bioinformatics where inherently a large number of items need to be managed, such as blood banks, stem cell banks, sperm banks, and DNA sequence banks.
For example, barcode technology is currently used for blood bank information systems, allowing safe blood donation and transfusion service that involve collecting, processing, storing, and providing human blood intended for transfusion. Incorrect blood component transfusion is the most frequent serious incident associated with transfusion. Errors which underlie these incidents frequently are attributed to sample misidentification. In face of the accelerating globalization, it is critical to track and manage an extremely large number of blood samples. However, for proper identification, barcode technology requires a significant amount of information to be encoded, such as including the patient's hospital number, last name, first name, date of birth, gender, blood type, and so forth. The need for this much information challenges the speed of present day scanners, especially when a probed barcode must be compared with a large database. This translates into a trade-off between scan speed and accuracy.
Accordingly, a need exists for a system and method of reading barcodes and performing displacement sensing in less time without the need of traversing the light over the item to be scanned. These needs and others are met within the present invention, which overcomes the deficiencies of previously developed scanning systems and methods.